A ball pen is a writing instrument. Ink filled in an ink cartridge received in a barrel of the ball pen flows to a metal ball at a tip of the pen under the action of atmospheric pressure and gravity of ink. The metal ball rotates when the ball pen is used to write on paper, and ink is transferred from the rotating metal ball to the paper to form handwriting strokes. Currently, click ball pens are very common in the market. By clicking downward on the top of the ball pen, the tip of the ink cartridge is extended from a bottom opening of the barrel or retracted into the barrel.
To allow the tip of the ink cartridge to project from the bottom opening of the barrel, the bottom opening of the barrel has a size slightly larger than a diameter of the ink cartridge. When the tip of the ink cartridge is forward extended from the barrel, there is a clearance formed between the ink cartridge and the bottom opening of the barrel. Due to the clearance, the tip of the ink cartridge extended from the barrel tends to incline while pressing against the bottom opening of the barrel. The inclined tip would possibly cause the forming of undesired handwriting strokes when using the click ball pen to write.
In view of the above disadvantage of the currently available ball pens, it is desirable to develop an improved ball pen, so that the tip of the ink cartridge extended from the bottom opening of the barrel can be continuously pressed against the bottom opening without inclining or swaying during the process of writing with the ball pen.